In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultra violet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) are the main light source used in mass production, and ArF excimer lasers (193 nm) are now also starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers (157 nm), EUV (extreme ultra violet radiation), and EB (electron beams) and the like as the light source (radiation source).
Resists for use with these types of short wavelength light sources require a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity relative to these types of short wavelength light sources.
One example of a known resist that satisfies these conditions is a chemically amplified resist, which includes a base resin and an acid generator (hereafter referred to as a PAG) that generates acid upon exposure. These chemically amplified resists include positive resists in which the alkali solubility of the exposed portions increases, and negative resists in which the alkali solubility of the exposed portions decreases.
Until recently, polyhydroxystyrene (PHS) or PHS-based resins in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups, which exhibit a high degree of transparency relative to a KrF excimer laser (248 nm), have been used as the base resin of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency relative to light with a wavelength shorter than 248 nm, such as light of 193 nm, is inadequate. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 nm. As a result, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as the base resin for resists that use ArF excimer laser lithography or the like, as they offer excellent transparency in the vicinity of 193 nm (for example, see patent reference 1).
In addition to favorable levels of sensitivity and resolution, these types of resists also require favorable levels of other lithographic properties such as depth of focus (DOF) and resist pattern shape.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2003-167347